The present invention relates generally to motor vehicle wheel balancing equipment. In particular, the present invention relates to a wheel balancer which continuously displays static imbalance while in the dynamic balancing mode.
It is well known that a vehicle wheel should be balanced prior to installation in order to improve ride quality and tire longevity. Two types of imbalance may be exhibited by the wheel: static imbalance and dynamic imbalance. Explained in terms of the reaction transmitted to the vehicle operator, static imbalance will cause the wheel to hop up and down as the vehicle is driven. This is very irritating to occupants of the vehicle, and only a small amount of static imbalance will become a noticeable vibration as the speed of the vehicle is increased.
Dynamic imbalance is a situation where the reaction by the rotating wheel is a wobble. A vehicle operator will feel this type of imbalance as a back and forth of the steering wheel from the front wheels, or as a seat shake left to right from the rear wheels. As a basic engineering fact, a tire and wheel that is perfectly dynamically balanced is statically balanced. However, a tire and wheel that is perfectly statically balanced is not necessarily dynamically balanced.
Originally, the only balancing systems available to the vehicle service industry were static-type bubble balancers. Many years ago, however, electronic wheel balancers were made available to dynamically balance automotive and truck wheels. After the introduction of the electronic balancers, the after-market industry moved rapidly to embrace this solution as a corrective measure for vehicle vibration. Vehicle manufacturers subsequently adopted dynamic wheel balancing equipment for use at their factories.
A typical electronic wheel balancer sold for after-market use is a two plane machine which resolves the imbalance vector into a corrective state by determining through calculations what amount of weight should be placed on the wheel flanges. Because a tire and wheel that is perfectly dynamically balanced is known to be statically balanced, operators of these machines have tended to rely exclusively on the dynamic balanced readout in determining that the tire is balanced.
However, as will be explained more fully below, situations exist where the machine will indicate dynamic balanced, but some static imbalance will remain. In such circumstances, the tire may tend to hop up and down as the vehicle is driven. Moreover, automotive manufacturers have recently concentrated on making their chassis increasingly stiff to reduce problems associated with chassis flex. A stiffer chassis, however, exacerbates wheel imbalance as felt by vehicle occupants. As a result, a slight imbalance is more likely to be noticed by a vehicle occupant. The cause of this vibration may be extremely difficult for the service technician to ascertain because the balancer itself indicated perfect dynamic balance.
The construction and operation of exemplary prior art wheel balancers are described in U.S. Pat. No. 5,337,256 to Cunningham and U.S. Pat. No. 5,311,777 to Cunningham, both of which are incorporated herein by reference.